The 22q11.2 deletion occurs in approximately 1 in every 2,000 to 4,000 live births, although this is likely a gross underestimate of its prevalence. It is thought to be almost as common as Down syndrome. In addition, it is the most frequent cause of syndromic palatal defects, and it is found in 1 of 68 children born with a heart defect. Despite this prevalence, many physicians are still not familiar with the diagnosis or its extreme variability. Because of this, a family may search for years for an explanation for a child’s problems, as well as for meaningful help. Sometimes patients are in their late teens or even adulthood when the diagnosis is made, and many people never get properly diagnosed at all.
There is a lot of confusion about various diagnoses given to children affected by the deletion. Other names that have been used for the 22q11.2 deletion include DiGeorge syndrome, velocardiofacial syndrome (VCFS), conotruncal anomaly face syndrome, Opitz G/BBB syndrome, and Cayler cardiofacial syndrome. These are all older names given to a collection of findings by different sub-specialists before anyone knew about the true cause of the various findings – the chromosome 22q11.2 deletion. For example, Angelo DiGeorge, MD, an endocrinologist, focused on problems with calcium; Robert Shprintzen, Ph.D, a speech pathologist, concentrated on palatal differences; and Dr. Kinouchi and others in Japan looked at heart defects. In 1997, Donna McDonald-McGinn, MS, CGC likened this phenomenon to a group of near-sighted veterinarians trying to describe an elephant by each examining a separate part. Each was accurate in describing his or her own area of interest, but none was able to see the big picture; so too was the case of the 22q11.2 deletion prior to the availability of a laboratory test for this chromosomal deletion. We now know that children with velocardiofacial, DiGeorge, conoctruncal anomaly face, Opitz G/BBB, and Cayler cardiofacial syndromes all have the same condition: the 22q11.2 deletion syndrome.
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Genetic testing to confirm the 22q11.2 deletion is usually done from a simple blood sample sent to a clinical lab. The recommended test today involves methods that are more sophisticated than the previously used fluorescence in situ hybridization (FISH) as the new tests also can tell the size of the deletion or duplication. These include “genome-wide” method such as comparative genomic hybridization (CGH), a SNP microarray (e.g., CGA) or MLPA test. Again, targeted FISH studies can miss some smaller “nested” 22q11.2 deletions/duplications that the more sophisticated methods will detect. A standard cytogenetic test (karyotype) is only very rarely able to detect the 22q11.2 deletion in about 25% of cases and is therefore not a recommended method for detecting 22q11.2DS.
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Most times, the deletion is not hereditary or “running in the family,” and parents without the deletion are not at increased risk of having a second affected child. However, a person with the deletion has a 50% chance of passing it on to his or her child with every pregnancy. In addition, as the findings in people with the 22q11.2 deletion are so variable, it is impossible to predict how mildly or significantly affected a child will be. It is important for parents to keep in mind that nothing they did or failed to do could have caused the deletion to occur. It is common for parents to initially feel a sense of guilt over the fact that their child has a “genetic condition,” but it is clear that this was out of their control and not anyone’s fault.